Tyrannosaur Repair

BDB · May 23, 2016

So....I crashed my Binder Design Tyrannosaur on its second flight this weekend. It flew perfectly to ~2,400 ft and then came down without deploying the main chute. The fault is entirely mine--I didn't use the DD altimeter correctly--which is why the following pictures are so painful.

The main damage site is one fin which has been completely knocked loose, though it is still in one piece. The airframe behind this fin slot is also damaged at the site where it butts up against the thrust ring.

Several of the other fins have cracked external filets, but they appear to still be firmly attached to the MMT and airframe.

Finally, the airframe just in front of the AV bay appears to have flexed during the hard landing. It still feels solid, but appears to be damaged along the tube's spiral.

I'm pretty sure that I can fix the aft section of the airframe and the broken fin with a bunch of epoxy and a ring clamp. I can also sand the cracked filets off and reform them with Rocketpoxy. But is that entirely necessary? Could I just sand them a little and then fill the cracks with a thinner epoxy, like BSI 30?

I am the most nervous about the front of the airframe. It feels sturdy, but I don't want it to flex again during flight. I would just jam a coupler down there and call it fixed, but that may not be an option because the "damaged" area overlaps with the AV bay by about 1/2".

I'm open to any and all advice (and condolences).

K'Tesh · May 23, 2016

Sorry to see such a cool rocket damaged so badly.

I think I'd go with 2x JLCR for mains deployment, and skip a 2nd event.

I hope you'll be able to get this back up and flying again soon.

Binder Design · May 24, 2016

BDB said:
I can also sand the cracked filets off and reform them with Rocketpoxy. But is that entirely necessary? Could I just sand them a little and then fill the cracks with a thinner epoxy, like BSI 30?

Sorry to see this! You can fill the fillet cracks with thin CA, then sand smooth. On the airframe, I'd cut it back to the undamaged section, then couple a new piece of airframe to it.

soopirV · May 24, 2016

BDB said:
So....I crashed my Binder Design Tyrannosaur on its second flight this weekend. It flew perfectly to ~2,400 ft and then came down without deploying the main chute. The fault is entirely mine--I didn't use the DD altimeter correctly--which is why the following pictures are so painful.

The main damage site is one fin which has been completely knocked loose, though it is still in one piece. The airframe behind this fin slot is also damaged at the site where it butts up against the thrust ring.

View attachment 291864 View attachment 291867

Several of the other fins have cracked external filets, but they appear to still be firmly attached to the MMT and airframe.

View attachment 291865

Finally, the airframe just in front of the AV bay appears to have flexed during the hard landing. It still feels solid, but appears to be damaged along the tube's spiral.

View attachment 291866 View attachment 291868

I'm pretty sure that I can fix the aft section of the airframe and the broken fin with a bunch of epoxy and a ring clamp. I can also sand the cracked filets off and reform them with Rocketpoxy. But is that entirely necessary? Could I just sand them a little and then fill the cracks with a thinner epoxy, like BSI 30?

I am the most nervous about the front of the airframe. It feels sturdy, but I don't want it to flex again during flight. I would just jam a coupler down there and call it fixed, but that may not be an option because the "damaged" area overlaps with the AV bay by about 1/2".

I'm open to any and all advice (and condolences).

Sorry to hear of your loss, was a great build to watch, but it looks entirely repairable! Do you mind sharing with the rest of us what went wrong with your electronics? I know that's probably a hard thing to discuss, but it ultimately would be the most helpful!

emckee · May 24, 2016

For the section of airframe forward of the AV bay, isn't this just a length of 4" (?) cardboard tube? Wouldn't it be easiest just to replace the section of tube entirely?

Normally I'd recommend the coupler method, but if the AV bay impinges on the damaged area, your major options are to add external reinforcement or to replace the damaged portion, either partially or entirely. Since the section of tubing is not a complex part, I'd just do the whole bit.

my 2 cents...

BDB · May 24, 2016

emcee...I just emailed Mike at Binder Design to ask about that very thing.

soopirV....here's my confession. I was flying with an Eggtimer TRS which was being controlled by the Eggfinder LCD remote. This was my first time flying with it. I had worked through all of the menu options multiple times to test the ejection charges and to practice programing the drogue and main settings--with one glaring exception....I hadn't actually practiced the "flight" menu.

So on the day of the flight, I entered my settings (drogue at nose over and main at 500') and told the Eggtimer that I was ready to fly. It displayed my settings on the LCD remote and indicated that the drogue and main chutes were "ON", so I walked away from the pad and the LCO hit the button......

I should have read the instructions more carefully. After seeing that both the ejection charges were "ON", I was supposed to acknowledge that I was ready to fly by holding the button on the LCD remote for ~7 seconds. I don't know why I didn't practice the flight sequence the week before. I even suspected that I might have some issues prepping for the flight, so I brought the Eggfinder's instructions with me to the launch, but then Go Fever took over and I left them sitting on my prep table...unopened.

I could barely sleep the next night--I was so mad at myself.

mattvd · May 25, 2016

Brenton,

Once you reset the fins in place I would recommend injecting some 2-part expanding foam into the rear of the MMT. That will give you some added strength to all the fins without the need to remove the other two. Email me if you want to discuss.

Matt

soopirV · May 25, 2016

BDB said:
emcee...I just emailed Mike at Binder Design to ask about that very thing.

soopirV....here's my confession. I was flying with an Eggtimer TRS which was being controlled by the Eggfinder LCD remote. This was my first time flying with it. I had worked through all of the menu options multiple times to test the ejection charges and to practice programing the drogue and main settings--with one glaring exception....I hadn't actually practiced the "flight" menu.

So on the day of the flight, I entered my settings (drogue at nose over and main at 500') and told the Eggtimer that I was ready to fly. It displayed my settings on the LCD remote and indicated that the drogue and main chutes were "ON", so I walked away from the pad and the LCO hit the button......

I should have read the instructions more carefully. After seeing that both the ejection charges were "ON", I was supposed to acknowledge that I was ready to fly by holding the button on the LCD remote for ~7 seconds. I don't know why I didn't practice the flight sequence the week before. I even suspected that I might have some issues prepping for the flight, so I brought the Eggfinder's instructions with me to the launch, but then Go Fever took over and I left them sitting on my prep table...unopened.

I could barely sleep the next night--I was so mad at myself.

Thanks for sharing- I have had failures like that too, and it always stings. All of my equipment is from Eggtimer (Three Eggtimers, two with WiFi Switches, and one Quantum, + 2 GPS) but I haven't yet tried a Dual Deployed flight. That was where my curiosity was coming from, not from a morbid curiosity, hope I didn't come across that way!

BDB · Jul 4, 2016

I took Matt's advice and used expanding foam to reinforce the fin can. I drilled six 1/4" holes, one for each "compartment" in the fin can. I then injected ~15 g of 2 part foam immediately after mixing into each hole using a 20 cc syringe.

(For anyone trying to copy the technique...Don't suck the mixture into the syringe. Pull out the plunger, and pour the foam mix into the syringe body. Then insert the plunger and inject into the hole.)

So here's the new problem....

ImageUploadedByRocketry Forum1467668287.938738.jpg

The foam expanded like crazy, and in so doing, pushed one set of the split fins out of alignment. (Ironically, not the one that had broken off.) Despite this, the fins feel very secure, so I don't think I will lose them during flight. I suspect that the rocket will just spin during flight, which I can definitely live with. Do I have any bigger problems than that?

BDB · Jul 5, 2016

For anyone interested in seeing what the foam looked like as it spewed out of the fin can holes....

Steve Shannon · Jul 5, 2016

To avoid that in the future, add the foam mixture in several small lifts, allowing each to expand before mixing the next.

[emoji1010] Steve Shannon [emoji1010]

K'Tesh · Jul 5, 2016

I'm also wondering if the fins were locked in place by a guide (much like the fin alignment guide from Payloadbay.com) while the foam sets up, would that prevent the fin from shifting?

To undo the shift, I also think if you can find a solvent that would dissolve the foam you might get a 2nd chance of re-aligning it. Then again, you'll have to deal with all the issues caused by injecting solvents.

BDB · Jul 5, 2016

K'Tesh said:
I'm also wondering if the fins were locked in place by a guide (much like the fin alignment guide from Payloadbay.com) while the foam sets up, would that prevent the fin from shifting?

I thought of that too--after it was too late. I even had an alignment guide that I made out of hardboard that would have worked great. :facepalm:

Binder Design · Jul 5, 2016

BDB said:
I suspect that the rocket will just spin during flight, which I can definitely live with. Do I have any bigger problems than that?

It will likely corkscrew on the way up.

Steve Shannon · Jul 5, 2016

K'Tesh said:
I'm also wondering if the fins were locked in place by a guide (much like the fin alignment guide from Payloadbay.com) while the foam sets up, would that prevent the fin from shifting?

To undo the shift, I also think if you can find a solvent that would dissolve the foam you might get a 2nd chance of re-aligning it. Then again, you'll have to deal with all the issues caused by injecting solvents.

There is no safe solvent that dissolves urethane foam once it has cured. Mechanical means are effective.

From the US Composites site:

15. Can I dissolve this foam once it has fully cured?

No. This foam is designed to be completely solvent resistant once cured. Gasoline and acetone will not cause any destruction of this foam. Please prepare ahead of time by covering any objects/areas that you do not want to come in contact with this highly adhesive product. If you do happen to spill some foam and it cures you will have to either sand or scrape the product away.

BDB · Nov 13, 2016

I just thought I'd report that this repair was 100% successful. After months of scheduling conflicts, I finally flew the repaired Tyrannosaur yesterday on a I405. Much to my surprise, it flew perfectly straight--no corkscrew. The only issue now is that the foam added considerable weight, so I have to fly with high-thrust motors, and I should probably invest in a larger main chute.

And I got the dual deploy monkey off my back! It's amazing how well the Eggtimer TRS works when you actually put it into flight mode. :facepalm:

Lowpuller · Nov 13, 2016

Awesome job.

What software did you use with the TRS to get this graph?

BDB · Nov 13, 2016

I haven't downloaded the data from the TRS yet. This graph is from my Jolly Logic Altimeter 3. I threw it in the AV bay just because I love being able to walk up to the rocket, connect via bluetooth, and download the data while walking back to the flight line.

K'Tesh · Nov 14, 2016

Congrats on the successful flight!

Forever_Metal · Nov 14, 2016

BDB said:
I just thought I'd report that this repair was 100% successful. After months of scheduling conflicts, I finally flew the repaired Tyrannosaur yesterday on a I405. Much to my surprise, it flew perfectly straight--no corkscrew. The only issue now is that the foam added considerable weight, so I have to fly with high-thrust motors, and I should probably invest in a larger main chute.

And I got the dual deploy monkey off my back! It's amazing how well the Eggtimer TRS works when you actually put it into flight mode.

View attachment 305296

congrats on the flight!

fm

Binder Design · Nov 14, 2016

Congrats! Thank you for flying Binder Design!

Tyrannosaur Repair

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